Layer 2 protocol in a cellular communication system

ABSTRACT

A method for transmitting messages using an efficient communications link protocol over an air interface of a cellular communications system is disclosed. A frame in the protocol is divided into a plurality of sections including a header section and a data section. The header section contains a field which indicates what type of information is contained in the frame.

This application is a divisional, of Application Ser. No. 08/474,902,filed Jun. 7, 1995 now U.S. Pat. No. 5,655,215 which is a divisional ofApplication No. 08/331,816, filed on Oct. 31, 1994; now U.S. Pat No.5,603,081 which is a continuation in part of U.S. patent applicationSer. No. 08/147,254, entitled “A Method for Communicating in a WirelessCommunication System,” which was filed on Nov. 1, 1993, now U.S. Pat.No. 5,603,081 and which is incorporated in this application byreference.

BACKGROUND

The present invention relates to a method for transmitting messagesbetween mobile stations and a central switching system, and moreparticularly to a method for transmitting these messages using a moreefficient communications link protocol over the air-interface of acellular telephone system.

In a typical cellular radio system, a geographical area, e.g., ametropolitan area, is divided into several smaller, contiguous radiocoverage areas called “cells” . The cells are served by a series offixed radio stations called “base stations” . The base stations areconnected to and controlled by a mobile services switching center (MSC).The MSC, in turn, is connected to the land-line (wire-line) publicswitched telephone network (PSTN). The telephone users (mobilesubscribers) in the cellular radio system are provided with portable(hand-held), transportable (hand-carried) or mobile (car-mounted)telephone units (mobile stations) which communicate voice andlor datawith the MSC through a nearby base station. The MSC switches callsbetween and among wire-line and mobile subscribers, controls signallingto the mobile stations, compiles billing statistics, and provides forthe operation, maintenance and testing of the system.

FIG. 1 illustrates the architecture of a conventional cellular radiosystem built according to the Advanced Mobile Phone Service (AMPS)standard. In FIG. 1, an arbitrary geographic area is divided into aplurality of contiguous radio coverage areas, or cells, CL1-C10. Whilethe system of FIG. 1 is, for illustration purposes, shown to includeonly ten cells, the number of cells may be much larger in practice.Associated with and located in each of the cells C1-C10 is a basestation designated as a corresponding one of a plurality of basestations B1-B10. Each of the base stations B1-B10 includes a pluralityof channel units, each comprising a transmitter, a receiver and acontroller, as is well known in the art.

In FIG. 1, the base stations B1-B10 are located at the center of thecells C1-C10, respectively, and are equipped with omni-directionalantennas transmitting equally in all directions. In this case, all thechannel units in each of the base stations B1-B10 are connected to oneantenna. However, in other configurations of the cellular radio system,the base stations B1-B10 may be located near the periphery, or otherwiseaway from the centers of the cells C1-C10 and may illuminate the cellsC1-C10 with radio signals directionally. For example, the base stationmay be equipped with three directional antennas, each one covering a120-degree sector cell as shown in FIG. 2. In this case, some channelunits will be connected to one antenna covering one sector cell, otherchannel units will be connected to another antenna covering anothersector cell, and the remaining channel units will be connected to theremaining antenna covering the remaining sector cell. In FIG. 2,therefore, the base station serves three sector cells. However, it isnot always necessary for three sector cells to exist and only one sectorcell needs to be used to cover, for example, a road or a highway.

Returning to FIG. 1, each of the base stations B1-B10 is connected byvoice and data links to an MSC 20 which is, in turn, connected to acentral office (not shown) in the public switching telephone network(PSTN), or a similar facility, e.g., an integrated system digitalnetwork (ISDN). The relevant connections and transmission modes betweenthe mobile switching center MSC 20 and the base stations B1-B10, orbetween the mobile switching center MSC 20 and the PSTN or ISDN, arewell known to those of ordinary skill in the art and may include twistedwire pairs, coaxial cables, fiber optic cables or microwave radiochannels operating in either analog or digital mode. Further, the voiceand data links may either be provided by the operator or leased from atelephone company (telco).

With continuing reference to FIG. 1, a plurality of mobile stationsM1-M9 may be found within the cells C1-C10. Again, while only ninemobile stations are shown in FIG. 1, the actual number of mobilestations may be much larger in practice and will generally exceed thenumber of base stations. Moreover, while none of the mobile stationsM1-M9 may be found in some of the cells C1-C10, the presence or absenceof the mobile stations M1-M9 in any particular one of the cells C1-C10depends on the individual desires of each of the mobile subscnbers whomay travel from one location in a cell to another or from one cell to anadjacent or neighboring cell.

Each of the mobile stations M1-M9 includes a transmitter, a receiver, acontroller and a user interface, e.g., a telephone handset, as is wellknown in the art. Each of the mobile stations M1-M9 is assigned a mobileidentification number (MIN) which, in the United States, is a digitalrepresentation of the telephone directory number of the mobilesubscriber. The MIN defines the subscription of the mobile subscriber onthe radio path and is sent from the mobile station to the MSC 20 at callorigination and from MSC 20 to the mobile station at call termination.Each of the mobile stations M1-M9 is also identified by an electronicserial number (ESN) which is a factory-set, “unchangeable” numberdesigned to protect against the unauthorized use of the mobile station.At call origination, for example, the mobile station will send the ESNto the MSC 20. The MSC 20 will compare the received ESN to a “blacklist”of the ESNs of mobile stations which have been reported to be stolen. Ifa match is found, the stolen mobile station will be denied access.

Each of the cells C1-C10 is allocated a subset of the radio frequency(RF) channels assigned to the entire cellular system by the concernedgovernment authority, e.g., the Federal Communications Commission (FCC)in the United States. Each subset of RF channels is divided into severalvoice or speech channels which are used to carry voice conversations,and at least one paging/access or control channel which is used to carrysupervisory data messages, between each of the base stations B1-B10 andthe mobile stations M1-M9 in its coverage area. Each RF channelcomprises a duplex channel (bi-directional radio transmission path)between the base station and the mobile station. The RF channel consistsof a pair of separate frequencies, one for transmission by the basestation (reception by the mobile station) and one for transmission bythe mobile station (reception by the base station). Each channel unit inthe base stations B1-B10 normally operates on a preselected one of theradio channels allocated to the corresponding cell, i.e., thetransmitter (TX) and receiver (RX) of the channel unit are tuned to apair of transmit and receive frequencies, respectively, which is notchanged. The transceiver (TXIRX) of each mobile station M1-M9, however,may tune to any of the radio channels specified in the system.

In typical land-line systems, remote stations and control centers areconnected by copper or fiber optic circuits which have a data throughputcapacity and performance integrity that is generally significantlybetter than the data throughput capacity and performance integrityprovided by an air interface in a cellular telephone system. As aresult, the conciseness of overhead required to manage any selectedcommunication link protocol for land-line systems is of secondaryimportance. In cellular telephone systems, an air interfacecommunications link protocol is required in order to allow a mobilestation to communicate with a cellular switching system. Acommunications link protocol is used to initiate and to receive cellulartelephone calls.

The electromagnetic spectrum available for use by cellular telephonesystems is limited and is portioned into units called channels.Individual channels are used as communication links either on a sharedbasis or on a dedicated or reserved basis. When individual channels areused as communication links on a shared basis, multiple mobile stationsmay either listen to or contend for the same channels. In the contendingsituation, each shared channel can be used by a plurality of mobilestations which compete to obtain exclusive use of the channel for alimited period of time. On the other hand, when individual channels areused as communication links on a dedicated basis, a single mobilestation is assigned the exclusive use of the channel for as long as itneeds it.

The continued need to serve existing analog-only mobile stations has ledto the specification in IS-54B of an analog control channel (ACC) whichhas been inherited from the prior AMPS or the equivalent EIA/TIA-553standard. According to EIA/TIA-553, the analog forward control channel(FOCC) on the down-link from the base station to the mobile stationscarries a continuous data stream of messages (words) in the format shownin FIG. 3. Several different types (functional classes) of messages maybe transmitted on the analog FOCC. These messages include a systemparameter overhead message (SPOM), a global action overhead message(GAOM), a registration identification message (REGID), a mobile stationcontrol message, e.g., a paging message, and a control-filler message.The SPOM, GOAM and REGID are overhead messages which are intended foruse by all mobile stations in the coverage area of the base station.Overhead messages are sent in a group called an overhead message train(OMT). The first message of each OMT must always be the SPOM which istransmitted every 0.8±0.3 seconds.

The format of the analog FOCC shown in FIG. 3 requires an idle mobilestation listening to the FOCC to read all the messages transmitted ineach OMT (not just paging messages) even though the informationcontained in these messages may not have changed from one OMT to thenext OMT. This requirement tends to unnecessarily limit the mobilestation battery life. One of the goals of the next generation digitalcellular systems is to extend the “talk time” for the user, that is, thebattery life of the mobile station. To this end, U.S. patent applicationSer. No. 07/956,640 (which is incorporated here by reference) disclosesa digital FOCC which can carry the types of messages specified for theanalog FOCC, but in a format which allows an idle mobile station to readoverhead messages when locking onto the FOCC and thereafter only whenthe information has changed, and to enter “sleep mode” at all othertimes. While in sleep mode, the mobile station turns off most internalcircuitry and saves battery power.

The above-referenced U.S. patent application Ser. No. 07/956,640 showshow a digital control channel (DCC) may be defined alongside the digitaltraffic channels (DTC) specified in IS-54B. Referring to FIG. 4, ahalf-rate DCC would occupy one slot, while a full-rate DCC would occupytwo slots, out of the six slots in each time-division-multiple-access(TDMA) frame of duration 40 milliseconds (msec). For additional DCCcapacity, additional half-rate or full-rate DCCs may be defined in placeof the DTCs until there are no more available slots on the carrier (DCCsmay then be defmed on another carrier if needed). Each IS-54B RFchannel, therefore, can carry DTCs only, DCCs only, or a mixture of bothDTCs and DCCs. Within the IS-54B framework, each RF channel can have upto three full-rate DTCs/DCCs, or six half-rate DTCs/DCCs, or anycombination in-between, for example, one full-rate and four half-rateDTCs/DCCs.

In general, however, the transmission rate of the DCC need not coincidewith the half-rate and full-rate specified in IS-54B, and the length ofthe DCC slots may not be uniform and may not coincide with the length ofthe DTC slots. FIG. 5 shows a general example of a forward (or downlink)DCC configured as a succession of time slots 1, 2, . . . , N, . . .included in the consecutive time slots 1, 2, . . . sent on a carrierfrequency. These DCC slots may be defined on a radio channel such asthat specified by IS-54B, and may consist, as seen in FIG. 5 forexample, of every n-th slot in a series of consecutive slots. Each DCCslot has a duration that may or may not be 6.67 msec, which is thelength of a DTC slot according to the IS-54B standard. (There are sixDTC slots in each 40-msec TDMA frame.) Alternatively (and withoutlimitation on other possible alternatives), these DCC slots may bedefined in other ways known to one skilled in the art.

As shown in FIG. 5, the DCC slots may be organized into superframes andeach superframe may include a number of logical channels that carrydifferent kinds of information. One or more DCC slots may be allocatedto each logical channel in the superframe. The exemplary downlinksuperframe in FIG. 5 includes three logical channels: a broadcastcontrol channel (BCCH) including six successive slots for overheadmessages; a paging channel (PCH) including one slot for paging messages;and an access response channel (ARCH) including one slot for channelassignment and other messages. The remaining time slots in the exemplarysuperframe of FIG. 5 may be dedicated to other logical channels, such asadditional paging channels PCH or other channels. Since the number ofmobile stations is usually much greater than the number of slots in thesuperframe, each paging slot is used for paging several mobile stationsthat share some unique characteristic, e.g., the last digit of the MIN.

For purposes of efficient sleep mode operation and fast cell selection,the BCCH may be divided into a number of sub-channels. U.S. patentapplication Ser. No. 07/956,640 discloses a BCCH structure that allowsthe mobile station to read a minimum amount of information when it isswitched on (when it locks onto a DCC) before being able to access thesystem (place or receive a call). After being switched on, an idlemobile station needs to regularly monitor only its assigned PCH slots(usually one in each superframe); the mobile can sleep during otherslots. The ratio of the mobile's time spent reading paging messages andits time spent asleep is controllable and represents a tradeoff betweencall-set-up delay and power consumption.

Since each TDMA time slot has a certain fixed information carryingcapacity, each burst typically carries only a portion of a layer 3message as noted above. In the uplink direction, multiple mobilestations attempt to communicate with the system on a contention basis,while multiple mobile stations listen for layer 3 messages sent from thesystem in the downlink direction. In known systems, any given layer 3message must be carried using as many TDMA channel bursts as required tosend the entire layer 3 message.

The communication link protocol is commonly referred to as a layer 2protocol within the communications industry and its functionalityincludes the limiting or framing of higher level messages. Traditionallayer 2 protocol framing mechanisms or bit stuffing in flag charactersare commonly used in land- line networks today to frame higher layermessages, which are referred to as layer 3 messages. These layer 3messages may be sent between communicating layer 3 peer entitiesresiding within mobile stations and cellular switching systems.

For a better understanding of the structure and operation of the presentinvention, the digital control channel DCC may be divided into threelayers: layer 1 (physical layer), layer 2, and layer 3. The physicallayer (L1) defmes the parameters of the physical communications channel,e.g., RF spacing, modulation characteristics, etc. Layer 2 (L2) definesthe techniques necessary for the accurate transmission of informationwithin the constraints of the physical channel, e.g., error correctionand detection, etc. Layer 3 (L3) defines the procedures for receptionand processing of information transmitted over the physical channel.

FIG. 6 schematically illustrates pluralities of layer 3 messages 11,layer 2 frames 13, and layer 1 channel bursts, or time slots, 15. InFIG. 6, each group of channel bursts corresponding to each layer 3message may constitute a logical channel, and as described above, thechannel bursts for a given layer 3 message would usually not beconsecutive slots on an IS-54B carrier. On the other hand, the channelbursts could be consecutive; as soon as one time slot ends, the nexttime slot could begin.

Each layer 1 channel burst 15 contains a complete layer 2 frame as wellas other information such as, for example, error correction informationand other overhead information used for layer 1 operation. Each layer 2frame contains at least a portion of a layer 3 message as well asoverhead information used for layer 2 operation. Although not indicatedin FIG. 6, each layer 3 message would include various informationelements that can be considered the payload of the message, a headerportion for identifying the respective message's type, and possiblypadding.

Each layer 1 burst and each layer 2 frame is divided into a plurality ofdifferent fields. In particular, a limited-length DATA field in eachlayer 2 frame contains the layer 3 message 11. Since layer 3 messageshave variable lengths depending upon the amount of information containedin the layer 3 message, a plurality of layer 2 frames may be needed fortransmission of a single layer 3 message. As a result, a plurality oflayer 1 channel bursts may also be needed to transmit the entire layer 3message as there is a one-to-one correspondence between channel burstsand layer 2 frames.

As noted above, when more than one channel burst is required to send alayer 3 message, the several bursts are not usually consecutive burstson the radio channel. Moreover, the several bursts are not even usuallysuccessive bursts devoted to the particular logical channel used forcarrying the layer 3 message.

In light of the generally reduced data throughput capacity andperformance integrity afforded by an individual channel in a channelsharing situation in a cellular telephone environment, the selection ofan efficient air interface protocol to serve as the basis of thecommunication link becomes paramount.

Thus, there is a need for a layer 2 header which describes what iscontained in the time slot, how it is contained in the time slot and howthe information should be interpreted.

SUMMARY

It is an object of the present invention to provide an indication withinthe layer 2 protocol which indicates what is contained in a time slot,how it is contained in a time slot and how the information should beinterpreted. According to one embodiment of the present invention, amethod for transmitting information to a mobile station from a cellularswitching system wherein a frame is divided into a plurality of sectionsincluding a header section and the header section is then coded so asto. identify what is contained in the frame.

According to another embodiment of the present invention, a cellularcommunications system can page a mobile station using a SPACHNotification message. The SPACH Notification message asks the mobilestation if it is able to receive a message and also indicates what typeof message is going to be transmitted to the mobile station.

According to another embodiment of the present invention, a groupidentity field can be included in the SPACH layer 2 protocol. The groupidentity field indicates that a mobile is part of a group and enablesthe cellular communication system to page a plurality of mobiles withone page by including the group identity field in the SPACH layer 2protocol. Furthermore, the SPACH layer 2 protocol can also include a goaway flag which can be used to tell mobiles not to use a particularcell.

According to another embodiment of the present invention, a mobilestation can distinguish between broadcast control channel BCCH slots andSPACH slots within a superframe. One way to distinguish between thedifferent slots is to use a different cyclic redundancy check in thedifferent type slots.

In yet another embodiment of the invention, a method for providingreserved channels in a layer 2 protocol in a cellular communicationsystem includes the steps of providing a field in broadcast controlchannel overhead messages that indicates where reserved channels arelocated within a supertrame. According to another embodiment of thepresent invention, a group identity field (GID) can be included in theSPACH layer 2 protocol. The group identity field indicates that a mobileis part of a group. By using this group identity, the communicationsystem can page the entire group using one page.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be descnbed in more detail with referenceto preferred embodiments of the invention, given only by way of example,and illustrated in the accompanying drawings, in which:

FIG. 1 shows the architecture of a conventional cellular radio system;

FIG. 2 shows a three sector cell which may be used in the system shownin FIG. 1;

FIG. 3 shows the format of a forward analog control channel;

FIG. 4 shows the structure of a forward TDMA channel according toIS-54B;

FIG. 5 is a generalized view of a digital control channel having timeslots which are grouped into superframes;

FIG. 6 illustrates a plurality of layer 3 messages, layer 2 frames, andlayer 1 channel bursts in a communication system;

FIG. 7 illustrates a block diagram of an exemplary cellular mobile radiotelephone system;

FIG. 8 illustrates the logical channels which make up the digitalcontrol channel according to one embodiment of the present invention;

FIG. 9 shows a hyperframe structure;

FIGS. 10 a-10 o illustrate various SPACH layer 2 protocol framesaccording to one embodiment of the present invention; and

FIG. 11 shows an exemplary slot format on the forward DCC.

DETAILED DESCRIPTION

Although the description hereinafter focuses on systems which complywith IS-54 B, the principles of the present invention are equallyapplicable to a variety of wireless communication system, e.g., cellularand satellite radio system, irrespective of the particular mode ofoperation (analog, digital, dual-mode, etc.), the access technique(FDMA, TDMA, CDMA, hybrid FDMATDMA/CDMA, etc.), or the architecture(macrocells, microcells, picocells, etc.). As will be appreciated by oneskilled in the art, the logical channel which carries speech and/or datamay be implemented in different ways at the physical channel level(layer 1). The physical channel may be, for example, a relatively narrowRF band (FDMA), a time slot on a radio frequency (TDMA), a code sequence(CDMA), or a combination of the foregoing. For purposes of the presentinvention, the term “channel” means any physical channel which can carryspeech and/or data, and is not limited to any particular mode ofoperation, access technique or system architecture.

This application contains subject matter which is related to U.S. Pat.No. 5,353,332 to Raith et al., entitled “Method and Apparatus forCommunication Control in a Radiotelephone System”; to U.S. patentapplication Ser. No. 071956,640, entitled “Digital Control Channel,”filed on Oct. 5, 1992; to U.S. patent application Ser. No. 08/047,452,entitled “Layer 2 Protocol for the Random Access Channel and the AccessResponse Channel,” filed on Apr. 19, 1993; to U.S. patent applicationSer. No. 08/147,254, entitled “A Method for Communicating in a WirelessCommunication System,” filed on Nov. 1, 1993; to U.S. patent applicationSer. No. 07/967,027, entitled “Multi-Mode Signal Processing,” filed onOct. 27, 1992; and to U.S. patent application Ser. No. 08/140,467entitled “A Method of Effecting Random Access in a Mobile Radio System,”filed on Oct. 25, 1993. These six co-pending applications areincorporated herein by reference.

FIG. 7 represents a block diagram of an exemplary cellular mobileradiotelephone system according to one embodiment of the presentinvention. The system shows an exemplary base station 110 and a mobilestation 120. The base station includes a control and processing unit 130which is connected to the MSC 140 which in turn is connected to the PSTN(not illustrated). General aspects of such cellular radiotelephonesystems are known in the art.

The base station 110 for a cell includes a plurality of voice channelshandled by voice channel receiver 150 which is controlled by the controland processing unit 130. Also, each base station includes a controlchannel transceiver 160 which may be capable of handling more than onecontrol channel. The control channel transceiver 160 is controlled bythe control and processing unit 130. The control channel transceiver 160broadcasts control information over the control channel of the basestation or cell to mobiles locked to that control channel.

When the mobile 120 is in an idle mode, the mobile periodically scansthe control channels of base stations like base station 110 to determinewhich cell to lock on or camp to. The mobile 120 receives absoluteinformation (information about the particular cell corresponding to thecontrol channel on which the information is being broadcast and mayinclude the service profile of that cell, the control channelorganization, and the type of cell) and relative information (generallythe same kind of information as absolute information but is informationconcerning the characteristics of other cells) broadcast on a controlchannel at its voice and control channel transceiver 170. Then, theprocessing unit 180 evaluates the received control channel informationwhich includes the characteristics of the candidate cells and determineswhich cell the mobile should lock onto. The received control channelinformation not only includes absolute information concerning the cellwith which it is associated, but also contains relative informationconcerning other cells proximate to the cell which the control channelis associated.

According to the present invention, the digital control channel DCCcomprises the logical channels shown in FIG. 8. The DCC logical channelsinclude: a broadcast control channel (BCCH), comprising a fast broadcastcontrol channel F-BCCH, an extended broadcast control channel E-BCCH,and a broadcast short-message-service control channel S-BCCH; ashort-message-service/paging/access channel SPACH, comprising apoint-to-point short-message-service channel (SMSCH), the paging channel(PCH), and an access response channel (ARCH); the random access controlchannel (RACH); and the reserved channel. The DCC slots can be organizedinto higher level structures called superframes as illustrated in FIG.5, or as preferably illustrated in FIG. 9, which depicts the framestructure of a forward (base station to mobile station) DCC and showstwo successive hyperframes, each of which preferably comprises arespective primary superframe and a respective secondary superframe.

Three successive superframes are illustrated in FIG. 9, each comprisinga plurality of time slots that are organized as the logical channelsF-BCCH, E-BCCH, S-BCCH, and SPACH. In general, one or more DCC slots maybe allocated for each logical channel in the superframe. Each superframein a forward DCC preferably includes a complete set of F-BCCHinformation (i.e., a set of layer 3 messages), using as many slots asare necessary, and each superframe preferably begins with a F-BCCH slot.After the F-BCCH slot or slots, the remaining slots in each superframeinclude one or more (or no) slots for the E-BCCH, S-BCCH, and SPACHlogical channels.

The BCCH, which in the example shown in FIG. 5 is allocated six DCCslots, carries overhead messages. One of the overhead messages is usedto define the end of the BCCH section within the superframe. The PCH,which is allocated one DCC slot, carries paging messages. The ARCH,which is also allocated one DCC slot, carries channel assignment andother messages. The exemplary superframe of FIG. 5 may contain otherlogical channels, including additional paging channels, as indicated byFIG. 9. If more than one PCH is defined, different groups of mobilestations identified by different traits may be assigned to differentPCHs.

The BCCH acronym is used to refer collectively to the F-BCCH, E-BCCH,and S-BCCH logical channels. These three logical channels are used, ingeneral, to carry generic, system-related information. The attributes ofthese three channels are that they are unidirectional (downlink),shared, point-to-multipoint, and unacknowledged. The fast BCCH is alogical channel used to broadcast time critical system information. Theextended BCCH is a logical channel used to broadcast system informationthat is less critical than the information sent on the F-BCCH. Thebroadcast short message service S-BCCH is a logical channel that is usedto broadcast short messages used for an SMS broadcast service.

The SPACH channel is a logical channel that is used to send informationto specific mobile stations regarding SMS point-to-point, paging and toprovide an access response channel. The SPACH channel may be consideredto be further subdivided into three logical channels: SMSCH, ARCH, andPCH. The paging channel PCH is a subset of the SPACH dedicated todelivering pages and orders. The access response channel ARCH is asubset of the SPACH to which the mobile station autonomously moves uponsuccessful completion of an access on the random access channel. TheARCH may be used to convey analog voice channel or digital trafficchannel assignments or other responses to the mobile access attempt. TheSMS point-to-point channel SMSCH is used to deliver short messages tospecific mobile stations receiving SMS services, although the messagescould also be addressed to more than one mobile. Similarly, the pagingmessages on the PCH may also be directed to more than one mobile. TheSPACH is unidirectional (downlink), shared, and unacknowledged. The PCHis generally point-to-multipoint, in that it can be used to send pagingmessages to more than one mobile station, but in some circumstances thePCH is point-to-point. The ARCH and SMSCH are generally point-to-point,although messages sent on the ARCH can also be addressed to more thanone mobile station.

For communication from the mobile stations to the base stations, thereverse (uplink) DCC comprises a random access channel RACH, which isused by the mobiles to request access to the system. The RACH logicalchannel is unidirectional, shared, point-to-point, and acknowledged. Alltime slots on the uplink are used for mobile access requests, either ona contention basis or on a reserved basis. Reserved-basis access isdescribed in U.S. patent application Ser. No. 08/140,467, entitled“Method of Effecting Random Access in a Mobile Radio System” , which wasfiled on Oct. 25, 1993, and which is incorporated in this application byreference. One feature of RACH operation is that reception of somedownlink information is required, whereby mobile stations receivereal-time feedback for every burst they send on the uplink. This isknown as Layer 2 ARQ, or automatic repeat request, on the RACH, and maybe provided by a flow of information called shared channel feedback on adownlink sub-channel.

It may be important sometimes to be able to distinguish between the BCCHslots and the SPACH slots within a superframe. For example, upon beingswitched on, a mobile station does not know which slots are BCCH slotsand which slots are SPACH slots. The mobile station needs to find theoverhead information at the beginning of the BCCH section to be able todetermine its paging slot. Also, the boundary between the BCCH sectionand the SPACH section may have changed for a variety of reasons. Forexample, if a system has been using twelve slots of a thity-two-slotsuperframe for the BCCH and wants to use thirteen slots for the BCCH,mobile stations assigned to the first paging slot after the BCCH slotsmust be informed that they should monitor another paging slot.

According to one aspect of the present invention, one way to distinguishbetween BCCH slots and SPACH slots is to use different cyclic redundancycheck (CRC) bits in these channels. For example, the CRC bits in theLayer 2 frames sent in the BCCH slots may be inverted, while the checkbits in the Layer 2 fames sent in the SPACH slots are not inverted.Thus, when a mobile reads the CRC bits, it obtains an indication of thekind of slot it has read. Using the check bits in this way isadvantageous in some situations where it is necessary to re-assign amobile station to another paging slot. The mobiles could obtain thisinformation by decoding one or two bits that would identify the type ofslot being decoded, but at a cost of reduced bandwidth. In Applicants'system, the mobile stations will recognize that something has changedwhen they spot the inverted CRC bits, and in response they will re-readthe F-BCCH, including the new DCC structure and paging slot assignment.

Furthermore, as illustrated in FIG. 8, the DCC logical channels mayinclude reserved channels that make the communication system moreflexible: new features, services, or functions can be added at a latertime without affecting existing mobiles. According to this embodiment ofthe present invention, the BCCH overhead messages include a field whichindicates where the reserved channels are located in the superframe.These reserved channels have a potentially wide variety of uses, such ascarrying messages specific to a system operator and/or mobile stationmanufacturer. While existing mobile stations may not be able to use thenew features described in the reserved channels, the existing mobilestations will take the location and number of reserved slots intoconsideration when determining the location of their respective pagingchannels.

The SPACH layer 2 protocol is used whenever a TDMA burst, or time slot,is used to carry point-to-point SMS, paging, or ARCH information. Asingle SPACH layer 2 protocol frame is constructed so as to fit within a125-bit envelope. An additional five bits are reserved for use as tailbits, resulting in a total of 130 bits of information carried withineach slot assigned for SPACH purposes. FIGS. 10 a-10 o show a range ofpossible SPACH layer 2 protocol frames under various conditions. Asummary of the possible SPACH formats is provided in the first tablebelow. A summary of the fields comprising layer 2 protocol frames forSPACH operation is provided in the second table below.

Similar frame formats are used for all SPACH channels such that allframes have a common Header A. The contents of the Header A determinewhether or not a Header B is present in any given SPACH frame. TheHeader A discriminates among hard page frames (containing no layer 3information), PCH frames, ARCH frames and SMSCH frames. A Hard TriplePage frame containing three 34-bit mobile station identifications(MSIDs) can be sent on the PCH (burst usage (BU) =Hard Triple Pace). AHard Quadruple Page frame containing four 20-bit or 24-bit MSIDs can besent on the PCH (BU =Hard Quadruple Page).

One or more L3 messages may be transmitted in one frame, or continuedover many frames. It is currently preferred that MSIDs are only carriedwithin frames where BU=PCH, ARCH or SMSCH with the burst type(BT)=Single MSID, Double MSID, Triple MSID, Quadruple MSID, or automaticretransmission request ARQ Mode BEGIN. The mobile station identity typeIDT field identifies the format of all MSIDs carried within a givenSPACH frame (i.e., no mixing of MSID formats is allowed). Pages carriedon the PCH are preferably not allowed to continue beyond a single SPACHframe, although the protocol allows for it. All other PCH messages maycontinue beyond a single SPACH frame.

For non-ARQ-mode operation, the L2 SPACH protocol supports sending asingle L3 message to multiple MSIDs in addition to the fixed one-to-onerelationship between MSIDs and L3 messages. A Message Mapping field (MM)is used to control this aspect of the layer 2 frame operation. A validSPACH frame requires that all L2 header information pertinent to a givenL2 frame be included entirely within that frame, i.e., the L2 headerfrom a given SPACH frame cannot wrap into another SPACH frame. An OffsetIndicator field (OI) is used to allow both the completion of apreviously started layer 3 message and the start of a new layer 3message to occur within a single SPACH frame.

The following table summarizes the possible SPACH formats:

CAN BE SMS PCH ARCH CONTINUED Single MSID Y Y Y Y Double MSID N Y Y YTriple MSID N Y Y Y Quadruple MSID N Y Y Y Hard Triple Page (MIN) N Y NN Hard Quadruple Page N Y N N (MINI) Continue Y Y Y Y ARQ Mode BEGIN Y NY Y ARQ Mode CONTINUE Y N Y Y Group ID Y Y Y Y

FIG. 10 a illustrates the SPACH Header A according to one embodiment ofthe present invention. The SPACH Header A contains burst usage (BU)information and flags for managing mobile stations in a sleep mode. TheBU field provides a high-level indication of burst usage. According tothe present invention, the operation performed on each SPACH channel isnot predetermined. The BU field indicates whether the burst is beingused for paging, access response, or short message services. The flagsindicate changes in sleep mode configuration as well as in broadcastcontrol channel information. This header is always present in allpossible SPACH frame types.

FIG. lOb illustrates the SPACH Header B according to one embodiment ofthe present invention. The SPACH Header B contains supplementary headerinformation used to identify the remaining contents of the layer 2frame. This header is present when Header A indicates a burst usage oftype PCH, ARCH or SMSCH. In one alternative, the bit used for the offsetindicator OI shown in FIG. 10 b as part of the Header B may be used as aSPACH response mode SRM indicator, i.e., as information about the layer2 access mode (contention or reservation) to be used in the next accessattempt made by the receiving mobile station. The SRM indicatorindicates how a mobile is to respond once it has received all framesassociated with a given SPACH message.

FIG. 10 c illustrates a Null Frame. The Null frame is sent whennecessary by the cellular system when there is nothing else to betransmitted for any given SPACH burst. The Null Frame also contains a GoAway GA flag which will be described below.

FIGS. 10 d, 10 e illustrate a Hard Triple Page Frame and a HardQuadruple Page Frame. A Hard Triple Page is a single frame page messagecontaining three 34-bit MINs. A Hard Quadruple Page is a single framepage message containing four 20-bit or 24-bit MINs as determined by themobile station identity type.

A Single MSID frame, as illustrated in FIG. 10 f, is used for startingthe delivery of ARCH or SMSCH L3 messages in a non-ARQ mode. Inaddition, this frame may also be used for sending L3 PCH messages (pagesor otherwise), which are non-ARQ by definition. Page messages sent usinga Single MSID frame cannot be continued into another frame.

If an ARCH or SMSCH L3 message is too long to fit into a Single MSIDframe then the remaining L3 information is carried using additionalCONTINUE frames or MSID frames as necessary. If a complete ARCH or SMSCHL3 message does fit within a Single MSID frame, it is padded withfiller, i.e., bits having a predetermined value like zero, as necessary.

If a non-page PCH L3 message is too long to fit into Single MSID framethen the remaining L3 information is carried using additional CONTINUEframes or MSID frames as necessary. If a complete PCH L3 message doesfit within a Single MSID frame, it is padded with FILLER as necessary. ADouble MSID frame, as illustrated in FIG. 10 g, is used for starting thedelivery of two ARCH messages in a non-ARQ mode or two PCH L3 messages.The number of MSIDs is indicated in the BT field with the same IDTformat used for both instances of MSID. Page messages sent using aDouble MSID frame cannot be continued into another frame. FIG. 10 hshows a Double MSID frame with continuation. FIG. 10 i shows a CONTINUEframe. FIG. 10 j shows an Offset Single MSID frame.

A Triple MSID frame, as illustrated in FIG. 10 k, is used for startingthe delivery of three ARCH L3 messages in a non-ARQ mode or three PCH L3messages. The number of MSIDs is indicated in the BT field with the samemobile station identity type format used for all instances of MSID. Pagemessages sent using a Triple MSID frame cannot be continued into anotherframe. A Quadruple MSID frame is used for starting the delivery of fourARCH L3 messages in non ARQ mode or four PCH L3 messages. The number ofMSIDs is indicated in the BT field with the same mobile station identitytype format used for all instances of MSID. Page messages sent using aQuadruple MSID frame cannot be continued into another frame.

A CONTINUE frame, as illustrated in FIG. 10 l, is used for continuationof the L3 messages which are too long to fit into the previous frame.Note that a L2 header which is specific to any given SPACH frame mustalways be carried entirely within that frame (i.e., the L2 headerassociated with a given SPACH frame is not completed by using asubsequent SPACH frame).

An ARQ Mode BEGIN frame, as illustrated in FIG. 10 m, is used forstarting the delivery of a L3 ARCH or SMSCH message in the ARQ mode. TheARQ Mode BEGIN frame contains only one MSID within its L2 header as wellas a portion of the L3 message itself. If the L3 message is too long tofit into a single ARQ Mode BEGIN frame, then the remaining L3information is carried using additional ARQ Mode CONTINUE frames asnecessary. If the L3 message does fit within a single ARQ Mode BEGINframe, it is padded with filler as necessary.

The PE field in conjunction with the transaction identifies TID fieldidentifies the transaction initiated by the ARQ Mode BEGIN frame andserves to associate any subsequent ARQ Mode CONTINUE frames with thissame transaction. An ARQ Mode BEGIN frame has an implicit frame numberFRNO value of zero associated with it.

The ARQ Mode CONTINUE frame, as illustrated in FIG. 10 n, is used forcontinuing a L3 ARCH or SMSCH message which is too long to fit into theprevious ARQ Mode frame (BEGIN or CONTINUE). The frame number FRNO fieldidentifies the CONTINUE frames within the context of the overall L3message. The FRNO field value is incremented for each CONTINUE framesent in support of a given transaction (i.e., multiple CONTINUE framesmay be sent to complete the transaction initiated by the ARQ Mode BEGINframe). The ARQ Mode Continue frame is also used to repeat anypreviously sent ARQ Mode CONTINUE frames received incorrectly by themobile station.

According to one embodiment of the present invention, a group identityfield (GID) can be included in the SPACH layer 2 protocol. The groupidentity field indicates that a mobile is part of a group. By using thisgroup identity, the communication system can page the entire group usingone page. A Group ID frame is illustrated in FIG. 10 o. The Group IDframe is used for starting the delivery of ARCH or SMSCH L3 messages ina non-ARQ mode. In addition, this frame may also be used for sending L3PCH messages (pages or otherwise), which are non-ARQ by definition. Pagemessages sent using a Group ID frame cannot be continued into anotherframe. If an ARCH or SMSCH L3 message or a non-page PCH L3 message istoo long to fit into a Group ID frame, then the remaining L3 informationis carried using an END frame or additional CONTINUE frames asnecessary. If a complete ARCH or SMSCH L3 message or a non-page PCH L3message does fit within a Group ID frame, it is padded with filler asnecessary.

According to another embodiment of the present invention, a go-away flagGA can be included in the SPACH layer 2 protocol for example in the NullFrame illustrated in FIG. 10 c. The GA flag can be used by the cellularsystem to indicate that the mobile stations should not attempt to use acertain cell. For example, this would permit a system operator to test abase station without risk of mobile stations trying to lock onto it. Thefollowing table summarizes the SPACH Layer 2 Protocol fields:

Length Field Name (bits) Values BU = Burst Usage 3 000 = Hard TriplePage (34 bit MSID) 001 = Hard Quad Page (20 or 24 bit MSID) 010 = PCHBurst 011 = ARCH Burst 100 = SMSCH Burst 101 = Reserved 110 = Reserved111 = Null PCON = PCH 1 0 = No PCH Continuation Continuation 1 = PCHContinuation, Activated BCN = BCCH 1 Transitions whenever there is aChange Notification change in F-BCCH information. SMSN = SMS 1Transitions whenever there is a Notification change in S-BCCHinformation. PFM = Paging Frame 1 0 = Use assigned PF Modifier 1 = Useone higher than assigned PF BT = Burst Type 3 000 = Single MSID Frame001 = Double MSID Frame 010 = Triple MSID Frame 011 = Quadruple MSIDFrame 100 = Continue Frame 101 = ARQ Mode Begin 110 = ARQ Mode Continue111 = Reserved IDT = Identity Type 2 00 = 20 bit TMSI 01 = 24 bit MINIper IS-54B 10 = 34 bit MIN per IS-54B 11 = 50 bit IMSI MSID = Mobile20/24/34/50 20 bit TMSI Station Identity 24 bit MINI 34 bit MIN 50 bitIMSI GID = Group Identity 24/34/50 24 bit MIN 1 34 bit MIN 50 bit IMSIMM = Message 1 0 = One instance of L3LI and Mapping L3DATA per instanceof MSID. 1 = One instance of L3LI and L3DATA for multiple MSIDs. OI =Offset Indicator 1 0 = No message offset included. 1 = Message offsetincluded. or SRM = SPACH 0 = Next access attempt made on Response ModeRACH to be contention-based. 1 = Next access attempt made on RACH to bereservation-based. CLI = Continuation 7 Number of bits remaining in theLength Indicator previous L3 message. GA = Go Away 1 Indicates if thecell is barred 0 = cell not barred 1 = cell barred L3LI = Layer 3 8Variable length layer 3 messages Length Indicator supported up to amaximum of 255 octets. L3DATA = Layer Variable Contains a portion (someor all) 3 Data of the layer 3 message having an overall length asindicated by L3LI. The portion of this field not used to carry layer 3information is filled with zeros. PE = Partial Echo 7 The 7 leastsignificant bits of the mobile station IS-54B MIN. TID = Transaction 2Indicates which ARQ mode Identity transaction is being transmitted onthe ARCH or SMSCH. FRNO = Frame 5 Uniquely identifies specific framesNumber sent in support of an ARQ mode transaction. FILLER = Burst FillerVariable All filler bits are set zero. CRC = Cyclic 16 Same Generatorpolynomial as IS- Redundancy Code 54B (includes DVCC)

According to the present invention, the mobile station can be in any ofa plurality of states. For example, a mobile station would be in a“start random acces” state before the first unit of a message that is tobe transmitted by a random access has been transmitted. The mobilestation would be in a “start reserved access” state before the firstunit of a message that is to be transmitted by a reservation-basedaccess has been transmitted. The mobile station would be in a “moreunits” state if there are more units associated with the same accessevent pending for transmission. The mobile station would be in a “afterlast burst” state if the last unit of an access event has beentransmitted. Finally, the mobile station would be in a “success” stateafter a message has been sent successfully.

The layer 2 protocol also provides for a plurality of flags. Forwardshared control feedback (SCF) flags are used to control the reversechannel, i.e., the RACH, as noted above. These SCF flags are a BRI flag,a R/N flag, and a CPE flag that are interleaved and transmitted in twofields in each downlink slot (layer 1); the total length of the twofields is twenty-two bits. A preferred information format in the slotsof the forward DCC is shown in FIG. 11. This format is substantially thesame as the format used for the DTCs under the IS-b 54B standard, butnew functionalities are accorded to the fields in each slot inaccordance with Applicants' invention. In FIG. 11, the number of bits ineach field is indicated above that field. The bits sent in the SYNCfield are used in a conventional way to help ensure accurate receptionof the CSFP and DATA fields, and the SYNC field would be the same asthat of a DTC according to IS-54B and would carry a predetermined bitpattern used by the base stations to find the start of the slot. TheCSFP field in each DCC slot conveys a coded superfrarne phase (SFP)value that enables the mobile stations to find the start of eachsuperframe.

The busy/reserved/idle (BRI) flag is used to indicate whether thecorresponding uplink RACH slot is Busy, Reserved or Idle forreserved-basis accesses, which is described in U.S. patent applicationSer. No. 08/140,467. Six bits are used for these flags and the differentconditions are encoded as shown in the table below:

BRI₅ BRI₄ BRI₃ BRI₂ BRI₁ BRI₀ Busy 1 1 1 1 0 0 Reserved 0 0 1 1 1 1 Idle0 0 0 0 0 0

The received/not received (R/N) flag is used to indicate whether or notthe base station received the last transmitted burst. A five-timesrepetition code is used for encoding this flag as shown in the tablebelow:

R/N₄ R/N₃ R/N₂ R/N₁ R/N₀ Received 1 1 1 1 1 Not Received 0 0 0 0 0

According to the present invention, partial echo information is used toidentify which mobile station was correctly received after the initialburst of random access and/or which mobile station is intended to haveaccess to the reserved slot. For example, the seven least significantbits of an IS-54B-type MIN can be assigned as the partial echoinformation, and these are preferably encoded in a manner similar to themanner in which the digital verification color code (DVCC) is encodedunder IS-54B, i.e., a (12,8) code, producing eleven bits of codedpartial echo information.

The following table shows how the mobile decodes received flagsaccording to the layer 2 state. Note that only the flags relevant to thelayer 2 state are shown. In the “start random access” state, the BRIflag is the only relevant flag. During a multiburst messagetransmission, both the BRI and R/N relevant. In the summary in thefollowing table, b_(i) is the bit value.

Received/Not Received Busy/Reserved/Idle Not Layer 2 State Busy ReservedIdle Received received 111100 001111 000000 11111 00000 Start randomaccess${{Idle}\quad {IF}{\sum\limits_{i = 1}^{4}\quad b_{i}}} < {2\quad {AND}{\sum\limits_{i = 3}^{6}\quad b_{i}}} < 2$

N/A N/A Start reserved Reserved IF < 3 bits difference to N/A N/A accessReserved flag code value More units Busy IF < 4 bits difference to Busyflag code value ${\sum\limits_{i = 1}^{5}\quad b_{i}} \geq 4$

${\sum\limits_{i = 1}^{5}\quad b_{i}} < 4$

After last burst Busy IF < 4 bits difference to Busy flag code value${\sum\limits_{i = 1}^{5}\quad b_{i}} \geq 4$

${\sum\limits_{i = 1}^{5}\quad b_{i}} < 4$

The mobile station interprets a received coded partial echo value ashaving been correctly decoded if it differs by less than three bits fromthe correct coded partial echo (CPE). This is referred to as PE match.

A mobile station is allowed a maximum of Y+1, where Y=(0, 1, . . . , 7),transmission attempts before considering the attempt to transfer amessage as a failure. The random delay period used in the mobile stationafter a Not Idle condition or after a transmission attempt is uniformlydistributed between zero msec and 200 msec with a granularity of 6.667msec (the duration of a time slot). A mobile station is preferably notallowed to make more than Z consecutive repetitions of an individualburst, where Z758 =(0, 1, . . . , 3).

According to one embodiment of the present invention, the BMI (basestation, mobile switching center and interworking function) can page amobile station by using SPACH Notification and thereby save much systembandwidth in some situations. For example, when a SPACH message is to bedelivered to a mobile in the system illustrated in FIG. 1, all ten basestations would transmit it since the system would generally not know inwhich cell the mobile was located. If the SPACH message required a totalof ten slots to transmit, 100 slots would be used by the system to sendthe SPACH message, ten slots per base station.

To avoid this waste, a SPACH Notification message would be broadcast inall ten cells, or whatever the appropriate number of cells for themobile station happened to be, rather than the entire SPACH message. Inessence, the SPACH Notification message asks the mobile station if it isable to receive a message. When the mobile station responds (on theRACH), the BMI can determine in which cell the mobile station is locatedand thus can send the SPACH message through that cell's base station.

In addition, the SPACH Notification message may also indicate what typeof SPACH message will be sent to the mobile station. For example, if themobile station receives a SPACH Notification which indicates that an SSD(Shared Secret Data) Update is coming, the mobile station issues aresponse containing a SPACH confirmation and starts a timer. The BMIthen transmits the SSD Update Order message. Upon receipt of themessage, the mobile stops the timer and enters the SSD Update ProceedingState. However, if the timer expires prior to receiving the SSD UpdateOrder message, the mobile returns to the DCCH camping state. The SPACHNotification could also be used to notify the mobile that a SMS messageis coming.

In another aspect, the system may dynamically assign temporary mobilestation identities (TMSIs) to the mobile stations. Such a TMSI would bea 20-bit or 24-bit MSID sent by the system over the air interface to amobile. The TMSI would be used by the network to page or deliver amessage to the corresponding mobile station on the SPACH, and the TMSIwould be used by the mobile station to make accesses on the RACH.

Using 20-bit TMSIs increases the paging capacity in comparison to using24 bit TMSIs at the expense of reducing the address space, i.e., thenumber of mobiles that can be paged, in the same way that using 24-bitMSIDs increases paging capacity in comparison to using 34-bit MINs(compare FIG. 10 e to FIG. 10 d, for example). As seen from FIG. 10 e ,a single layer 2 paging frame can carry five 20-bit TMSIs, or pages,instead of four 24-bit TMSIs (or MSIDs). By providing a plurality ofTMSI formats, one has the flexibility to trade off address space forpaging capacity.

It is currently preferred that the BMI assign a TMSI to a mobile inresponse to the mobile's registration, in which case the TMSI can beprovided in an information element called MSID Assignment that isincluded in a Registration Accept message sent on the SPACH.Advantageously, the mobile station would treat the assigned TMSI asvalid until it is switched off or until it decides to carry out any ofthe following system accesses: a new system registration; a forcedregistration; a power-up registration; a TMSI timeout registration; aderegistration registration; or the first system access of any kind madeafter receiving various other messages, such as a registration rejectmessage. A mobile station assigned a TMSI in a registration acceptmessage sent by the BMI using ARQ mode advantageously would only treatthe assigned TMSI as valid if the ARQ transaction were completedsuccessfully from a layer 2 perspective.

While a particular embodiment of the present invention has beendescribed and illustrated, it should be understood that the invention isnot limited thereto since modifications may be made by persons skilledin the art. The present application contemplates any and allmodifications that fall within the spirit and scope of the underlyinginvention disclosed and claimed herein.

We claim:
 1. A method for paging a plurality of mobile stations in acellular communication system, comprising the steps of: generating acommon header field; assigning said plurality of mobile stations a usergroup identification code; and broadcasting a paging message containingsaid common header field and said user group identification code inlayer 2 protocol overhead information for said paging message, whereinsaid common header field contains burst usage information and flags formanaging mobile stations in sleep mode.
 2. A cellular communicationsystem with a plurality of mobile stations and at least one basestation, comprising: means for generating a common header field; meansfor assigning a group of mobile stations a user group identificationcode; means for storing said user group identification code in saidmobile stations; and means for broadcasting a paging message containingsaid common header field and said user group identification code inlayer 2 protocol overhead information of said paging message, whereinsaid common header field contains burst usage information and flags formanaging the plurality of mobile stations in sleep mode.
 3. A mobilestation for use in a cellular communication system comprising: means forstoring a user group identification code, said user group identificationcode identifying said mobile station as being a member of a group ofmobile stations; means for receiving a paging message containing acommon header field and a user group identification code in layer 2protocol overhead information, wherein said common header field containsburst usage information and flags for managing the mobile station insleep mode; means for comparing said stored user group identificationcode with said received user group identification code; and means forresponding to said paging message when said user group identificationcodes match.
 4. The method of claim 1, wherein the paging message isbroadcast in a control channel.
 5. The method of claim 4, wherein thecontrol channel is a digital control channel.
 6. The method of claim 1,wherein the layer 2 protocol overhead information is in ashort-message-service paging/access channel (SPACH).
 7. The cellularcommunication system of claim 2, wherein the paging message is broadcastin a control channel.
 8. The cellular communication system of claim 7,wherein the control channel is a digital control channel.
 9. Thecellular communication system of claim 2, wherein the layer 2 protocoloverhead information is in a short-message-service paging/access channel(SPACH).
 10. The mobile station of claim 3, wherein the paging messageis received in a control channel.
 11. The mobile station of claim 10,wherein the control channel is a digital control channel.
 12. The mobilestation of claim 3, wherein the layer 2 protocol overhead information isin a short-message-service paging/access channel (SPACH).
 13. In awireless communication system, a method for providing information to amobile station, the method comprising: generating a common header field;generating a group identity field containing a group identity code foridentifying a mobile station as being a member of a group of mobilestations; generating at least another field containing information forthe mobile stations associated with the group identity code; andbroadcasting the common header field, the group identity field and theat least another field in a frame, wherein the frame is transmitted in acontrol channel and wherein the common header field contains burst usageinformation and flags for managing the mobile station in sleep mode. 14.The method of claim 13, wherein the control channel is a digital controlchannel.
 15. The method of claim 13, wherein the frame is used forstarting the delivery of access response channel (ARCH) messages. 16.The method of claim 13, wherein the frame is used for starting thedelivery of point-to-point short-message-service (SMSCH) channel layer 3messages.
 17. The method of claim 13, wherein the frame is used forsending layer 3 paging channel (PCH) messages.